1. Field of the Invention
This invention relates to a magnetic tape cassette such as used in a VTR or the like. This invention particularly relates to the structure of said case.
2. Description of the Prior Art
A magnetic tape cartridge generally consists of a cassette case which houses a pair of reels around which are wound magnetic tape. The cassette is inserted in a VTR or the like and the reels rotated to move the tape past the recording or playback head of the VTR for the recording or playback of voice signals, image signals, and the like. FIG. 1 is a plane view of an example of a conventional magnetic tape cartridge for use in a VTR. The cassette case consists of an upper half and a lower half, both formed of synthetic resin, and the view in the figure is that when the upper half has been removed. Disposed within the lower half of the cassette case 1 is a pair of reels 3a, 3b which are rotatable and around which are wound a magnetic tape 4. One end of the tape 4 is attached to the reel 3a and the other end is guided outside the case by guide pins 5a, 5b, across the front of the case parallel to the outer face portions 1a, 1b from which it is separated by a small space (not more than about 2 mm), feeds back into the case via guide pins 5c, 5d and thence is wound around reel 3b. The friction produced by a spring member 6 pressing the tape against the guide pin 5d keeps the tape taut by preventing any slack or looseness developing in the tape 4. Because the tape thus disposed parallel to the front faces 1a, 1b is exposed to the outside, the upper case 2 (not shown) is provided with an openable cover which covers the front of the case (in the figure, the lower face) to protect the tape against dust and damage.
When a cassette constructed thus is inserted into a VTR set for recording or playback, the reels 3a, 3b are rotated by a motor, transporting the tape 4 at the required speed for said recording or playback. Upon completion of the recording/playback the tape is rewound. Because the rewinding proceeds at a fairly high speed (e.g. 1.5 m/sec), there is a risk that the friction of any contact between the tape and the case will generate static electricity. This will also be the case during fast-forwarding of the tape. If the tape 4 is charged with static electricity, it will stick to the case because the case is made of synthetic resin, thereby hindering such rewinding/fast-forwarding. In particular, with reference to the cassette of FIG. 1, because the tape is separated from the front faces 1a, 1b by only a very small space, there is a strong likelihood that the tape will stick to these faces 1a, 1b. FIG. 2 is an enlarged plane view of the front portion of the cassette of FIG. 1, and FIG. 3 is a cross-section of the front along the arrows A--A. Although the tape 4 usually will run approximately parallel to the front faces 1a, 1b, 2a, 2b and at a small distance c (about 0.5-2 mm) therefrom, the space between the tape and the front faces is set only by the guide pins 5b and 5c, so that in the event that the tape becomes charged with static electricity the tape can easily stick to the front faces. This will require a greater motive force by the motor to transport the tape, or the tape may be unable to be moved, or may be transported while still sticking to the case, damaging the tape and causing the speed of the tape travel to become erratic.